I meant to ask for AP (pgr39) but I assume you would have thought that also.

In any case, I read it should be 740 m/s, 750m/s and 790 m/s (respectively). The L48 was supposed to be a higher velocity but there was some problem with the fluted cartridges getting stuck. The Germans supposedly backed off the powder charge on the L48 till the velocity was 750 m/s. Since the L43 and L48 share cartridges, I always wondered about this story.

The PAK40 did not share this fluted cartridge and had none of these issues. Some sources say it should be 770 m/s.

I meant to ask for AP (pgr39) but I assume you would have thought that also.

In any case, I read it should be 740 m/s, 750m/s and 790 m/s (respectively). The L48 was supposed to be a higher velocity but there was some problem with the fluted cartridges getting stuck. The Germans supposedly backed off the powder charge on the L48 till the velocity was 750 m/s. Since the L43 and L48 share cartridges, I always wondered about this story.

The PAK40 did not share this fluted cartridge and had none of these issues. Some sources say it should be 770 m/s.

Right you are. The US tested at least two Pak40s. One was at 790m/s and the other 774 m/s. Could be a different type load, wartime sub-par ammo or worn barrel.

The 'HK' is the better known Tungsten round. The 'W' is the 'soft' round. The HK was for better armored tanks and the W was for lighter armor or so it would seem. At the extreme velocity these weapons could produce, the W round could still do devastating damage. Against cast armor, it would have a great effect.

The PAK40 also had these rounds. Seemingly for faster moving lighter armor. Here is the Yugoslav test data:

M39 AP penetrates side turret @ 1750m M40 subcaliber penetrates side turret at any efective range M40W subcaliber penetrates side turret @ 200m M38B HEAT penetrates side turret if side angle is less then 30deg

*It apears that subcaliber (APCR/HVAP) suffered more from high hardness, largely sloped glacis... **That is a version of M40 subcaliber that had soft steel core. It was acording to the manuel to be used vs "fast, lightly armored targets"...

Apparently an updated Wiki of the 75mm Pak 40 has a reference to a 1955 US document: 'Foreign Military Weapons and Equipment (U) Vol. 1 Artillery (U) dated August of 1955'. Wiki says it corrects the muzzle velocity of the 1945 US tests of the gun. The new muzzle velocity is stated as 750 m/s. The penetration as stated is the same as the 75mm/L43 in the 'Encylopedia of German Tanks' . Viewing this 'recently declassified' document it is obvious that it is only a rehash of German data presented in yards and meters. Ten years after the fact and not of new tests it is a little dodgy.

To add weight to this the author Hilary Doyle tells the blogger at WOT it was reduced to 750 m/s.

But a recently released Soviet era document of tested ammo lists the 75mm Pak 40 velocity as 770m/s. This is similar to the 'US Handbook of German Weapons' listing it as 2530 f/s=771 m/s. So we have live tests of captured weapons showing it is either 770 or 792 m/s.

I would have to side with data from live tests over second hand documents. Or there were a wide variety of different quality rounds being made. (Which is possible.)

I would expect the AP rounds powder (which used the same projectile for the AP39 type round), to be similiarly different in powder weight. From my understanding, the L43 and L48 weapons had issues with the fluted 'brass' (or steel) cartridges not ejecting and the powder load was scaled back. The pak40 ATG did not have this issue with its strait designed cartridge. Basically, the PAK40 was a better tank killer. Therefore, AFV like the Marder series still had value almost to the end of the war.

That link in the text repeats that the charge was reduced to be 750 m/s later in the war to be more in common with the L/48 and L/43. But is at a loss to explain why captured L/46 guns (either by the US or USSR) tested out to have either 770 or 792 m/s.

I don't believe that would happen. Sights for direct fire weapons are specific in regards to muzzle velocity. I believe the PAK40 had it's own 3X sight? To suddenly have ammunition with a different performance means all kinds of training and other issues. PAK40 production, including Marder AFV, was something like 30K guns. Ammunition was probably in the millions. Trained gunners in the 100K range.

And as the war went on, and the T34 and Sherman, etc. got better armor; who would reduce the performance of this principal weapon if there were no outstanding issues?

I would like to see powder weight info on the PAK40 and KWK weapons. Since they both fired the same projectile, I would think this data would shed light on the issue. I swore I saw it somewhere but never captured it.

An interesting point is that since they both fired the same projectile, the KWK weapon had a projectile that was well over-rated and hardly ever shattered. If there was a decline in AP manufacturing quality, this might explain the retrograde movement of teh PAK40 velocity. But I believe that the Germans had excellent projectile quality as far as hardness etc.

This is what wiki and the other pdf is basing it on. It comes from that 1955 publication I mention above. If you check the data you find it is German data from datenblatts. Go to any Jentz book with gun data and it will match. Except there are a number of errors. The 88mm/L56 APCBC is switched with the APCR and a Japanese gun is included.

The Handbook on German Military Forces 1945 has the gun at 771 m/s and Russian data has it at 770 m/s. The Aberdeen tests have it as 792 m/s.

ORIGINAL: Yoozername hI have read somewhere that the KWK 75mm L48 had 2.41Kg

That could of course be the early round. Mid production they could of changed to a light charge.

If would be fun to speculate what that 770 m/s round is. Did it exist as a separate type or was it just a convenient average of 750 and 790 m/s of the only two rounds types we know? Germany’s enemies capturing mixed stocks of these rounds could of thought that German quality control had gone off the rails. Some rounds were hot some were weak-sisters.

Testing these rounds would be a puzzle. The US would have an easier time of it because of its criteria. The US uses a 50% penetration criteria. So it first has to establish the ballistics of the gun. Since they are going by the 50% rule the best rounds could be used as they are the best 50%. Once they decide on what the velocity at any point will be they can adjust the charge to attain that for at test vs. a particular armor plate. The US has the added test criteria that the rounds in a test must all be within 30 ft/s. So the charges are measured out to obtain this for a test. So they open up a round and replace what ever is in it. Also, when testing it only matters what the limit velocity the 50% penetrate are. It doesn’t matter if the 50% that don’t penetrate are partial penetrations, shatters or are paint. So the US testers get their data from the 50% best rounds and they move on.

The Soviets though may have been in a pickle. Their criteria is 80% of the hits must penetrate at a range. They get a mixed lot of shells to fire at a target. How are they going to find the 80% mark when maybe half the rounds go through the target like Swiss-cheese and the others fail? Well, they came up with something though.

In PCO we could make a mod for this. We could add an 'AP' round for the 75mm L/46 gun. This could be the weak round. Then give the Pak 40 half their loadout in say 1944+ in these rounds and half in the better APHE.

The Germans actually printed on the cartridge cases the 'pulver-weight'. I suppose going to the ammo collectors websites could find some detailed information. I saw some 75mmL48 ammunition at a site and they did indeed say 2.41 Kg. Again, the whole issue of having mixed ammunition and the gun-sight 'kludge' factoring makes me lean towards disbelief.

The Pak40 rounds were as long as the panther rounds. Most people claim this made using an adaption of the Pak40 gun into anything but Marder type vehicles impractical. But since the Panther 75mmL70 gun WAS used in JagdpanzerIV tank-destroyers, then there would be room for something like a PAK40 adaption in a JagdpanzerIV at least. It could have been used in StuGIV and possibly even StuGIII. Clearly, using StuGIII in infantry divisions would have been easier if they shared PAK40 ammunition. The extra anti-armor performance could be had without resorting to the extremely long panther gun. Personally I think that the StuGIII development, like the PanzerIV, was stalled out too early.

Real velocity testing would have to report variables like ambient temperature, ammunition temp, gun temp and a whole slew of other atmospheric information. Good luck trying to find all that information.

Accuracy of velocity measurement testing should be based on the technology of the time, chronograph instrumentation, and have an associated accuracy specification. But I would guess that they could measure +/- 5 meters a second, or less, for most tank and artillery weapons. Actually, there were mobile units that tested weapons in the field. Certainly anti-aircraft artillery was tested as part of maintenance.

The difference in 792 m/s and 750 m/s is fairly large. In terms of kinetic energy, the Pak40 would be 11.5% greater KE. That would be translational KE. There might still be a difference in rotational KE to be accounted for .

The US certainly met the PAK40 in North Africa first. The Germans had Tp. (tropical) ammunition types for weapons. Basically a reduced charge since the ammo was in warm ambient conditions. It's possible the US might have tested guns with 'hot' ammo in colder conditions etc.

ORIGINAL: Yoozername The Germans actually printed on the cartridge cases the 'pulver-weight'. I suppose going to the ammo collectors websites could find some detailed information. I saw some 75mmL48 ammunition at a site and they did indeed say 2.41 Kg. Again, the whole issue of having mixed ammunition and the gun-sight 'kludge' factoring makes me lean towards disbelief.

The ballistics of the same projectile at 750m/s and 792m/s isn't that different. There is a 55.7% chance of hitting a T-34 sized target at 1000 yd with the 792m/s projectile and a 52.5% chance of hitting the same T-34 sized target at 1000 yd with the 750m/s projectile. This with a first round ranging error of say 18%. The ranging error would produce a hit zone about +/- 136 yds long while the shells with different velocities would only fall about 45 yds apart.

Guns are 'zeroed' to match a lot of ammunition, a barrel and a sight. Once a weapon is zeroed, introducing ammunition that has either increased powder or reduced powder, negates that zeroing and must either be re-zeroed or some fudging is used in the sight. The fudging means adding range to the normal range if using a reduced charge. This isn't constant across all ranges. One would add little to nothing at very close range and progressively more for medium and longer range.

Yes, zeroing would be a problems. The Germans regularly zeroed their guns. But if the nerfed ammo was introduced after a certain date then all replacement ammo after that had the same ballistics. Guns in places where there was no fighting probably had the old ammo and never got the new type.

I would need some documentation that shows the 75mmL46 PAK40 AP39 rounds actually showed a decreased powder-weight reported on the cartridge case. To me, that would be compelling evidence.

The Germans explored alternatives for the Pak40 ammunition, see my earlier posts, and they seemed to have dropped these . Everyone knows the tungsten rounds were pulled by 1944. They also seemed to have given up on HEAT rounds for the PAK40. The 'soft-core' W rounds were probably just used by Marder units for fast moving AFV like light tanks and armored cars etc.

So, by 1944, the PAK40 had to rely on AP39 and HE shells. It certainly simplified training. But, to downgrade performance for what ends? Save gunpowder? I don't think so.

The PAK40, from my understanding, used different rifling than the KWK 75mmL48. The PAK used progressive rifling and the KWK used uniform rifling. Interestingly enough, the early KWK 75mmL43 also used progressive rifling. Some say the PAK40 and KWK L43 actually shared the same barrel.

My thought is that the initial KWK 75mmL43 used a higher propellant charge with little to no issues. It basically was limited in recoil length given that the commander sat behind the gun itself. But once the uniform twist barrel of the L48 was substituted for the L43, the weapon had issues with extraction possibly due to the initial pressure buildup the quicker onset of rifling introduced. The KWK solution was to reduce the charge to a level that allowed the weapon to work and still give acceptable penetration. A bad solution in my opinion but the Germans evidently wanted to produce L48 barrels quicker. I suppose the barrels would also last longer. This is not much of a concern with PAK weapons which fire much less rounds over their 'life-time'.

But I see no evidence besides mis-types as far as PAK40 m/v being lower later in the war. Certainly, armor penetration would be lower also.

I have seen that before at WK2ammo website. To be honest, it looks like someone's homework that was copied in a hasty manner.

Again, there is an issue here with the sight. If you notice the velocities for the HE and Tungsten rounds, they have not really changed. That is, 930 and 550 m/sec respectively. So , if the gun is actually zeroing with a 750 m/sec AP39 round, then the AP40 and HE are dependent on that AP39 round to set the sight. One does not fire a AP40 and certainly not a HE round when zeroing.

This again shows the need for a unique sight if the AP39 PAK40 round was degraded in performance.

Again, I would be more impressed if a Datenblatt for the round stated a velocity differential as well as stating a reduced charge.